Could be due to your ISP. But it might also be due to unreliable sources. Are you properly configured re: firewall & modem/router? Although the following link applies to LimeWire, it can also apply to other gnutella programs (with some exceptions): Connection problems? Check here first!

BTW this type of post should normally be posted in the appropriate client section; eg: BearShare or LimeWire or Morpheus, etc. depending on which one you're using.